In recent years, studies on an OCB cell that is to be used as a liquid crystal cell instead of a TN cell have been made. An OCB cell is in a splay orientation state when no bias voltage is applied thereto, and exhibits a bend orientation state when a given high voltage is applied thereto. And in the bend orientation state, top and bottom liquid crystal molecules are always oriented symmetrically, thus compensates for the birefringence of liquid crystal molecules so as to obtain the uniform viewing angle characteristic at all directions easily than with the orientation division method as well as a high-speed response characteristic that is one order faster than with conventional TN cells.
FIG. 1A shows a pixel structure plan diagram of a thin-film transistor LCD. The gate electrode 306a of the switch transistor 306 is connected to the scan line 302. The drain electrode 306b of the switch transistor 306 is connected to the pixel electrode 308 and the source electrode 306c is connected to the video data line 304. A common line 310 is used as the common electrode of the pixel electrode 308. The switch transistor 306 is usually a thin-film transistor (TFT) that is deposited on a transparent substrate such as glass. By scanning the scan lines 302 and in accordance with the scan signals, all of the switch transistors 306 in a given scan line 302 are turned on. At the same time, video signals are provided in the video data lines synchronously with the selected scan line 302.
FIG. 1B shows orientation state in accordance with the conventional method. The liquid crystal molecule 330 in the whole pixel is in splay state. In accordance with this method, a high voltage is applied between the conductor electrode 324 and the pixel electrode 308 for a given period at the start of operation of a liquid crystal display device using the OCB cell to transform the liquid crystal molecule 330 from splay state into the bend state. This fixed start time usually takes more than several tens of seconds. The liquid crystal molecule 330 returns to splay state when the LCDs is turned off. However, part of the liquid crystal molecule 330, such as the liquid crystal molecule between the video data line 304 and the pixel electrode 308, is applied to the high voltage and long duration in this mode, which causes two liquid crystal molecule states when the LCDs is turned on. Yet another problem is that even if the liquid crystal molecule 330 is transformed from splay orientation to bend orientation at the start of operation, the OCB cell may return to splay orientation during operation. The LCD must be restarted for display to return to normal.
On the other hand, recent battery-driven systems such as notebook-type personal computers equipped with a TFT color liquid crystal display device are increasingly required to be of a power-saving type. To conserve power, such a liquid crystal display device has a driving mode stop function to turn off a display thereof. Once the LCD is turned off, an OCB cell returns to splay orientation from bend orientation. A period of time is needed to restore the bend orientation state; thus the display cannot be turned on instantaneously.